It has already been proposed that semiconductor substrates be transported automatically into and out of heat treatment furnaces, which are generally tubular furnaces, with the aid of transport devices which feed the semiconductor substrates, contained in magazines of glass or ceramic, normally vitreous silica, horizontally into and out of the furnaces. A plurality of such tubular furnaces are often disposed in stacks one above the other, each furnace having its own loading device for the substrates.
Up to the present time, the semiconductor substrates have been conveyed manually to or from the horizontally movable transport device or loading device in order to load or unload the furnace; in other words, a human operator inserts or removes the magazines containing the semiconductor wafers one by one, with the aid of a special tool, such as a lifting fork. With increasing substrate size and hence additional weight, however, this type of operation is becoming increasingly impractical. Furthermore human operators must be kept away from the immediate vicinity of the furnace and the loading and unloading station, as much as possible, because these persons have been found to be a source of contamination, which impairs clean room conditions and reduces the efficiency of semiconductor production.
A conventional heat treatment apparatus is disclosed in German Patent Disclosure Document No. DE-OS 32 37 047 to which U.S. Pat. No. 4,468,195 corresponds. In this heat treatment apparatus, the semiconductor wafers that are to be treated, which are disposed in carriers, are fed into the tubular furnace and retrieved therefrom by using a fork, which is part of a stationary loading unit associated with each furnace. The fork can be raised and lowered for this purpose.